Keep a copy of "Mormons Answered Verse by Verse", by Reed & Farkas on your bookshelf.
It's designed to assist when the bicycle boys come to the door -- it has a listing of the Old Testament and New Testament verses they usually use to prove that they're a mainstream Christian religion, based on the Bible, and a refutation of the way they interpret those verses (that's the defense.) Then it goes on offense, giving a listing of verses from the Book of Mormon that show the book to be self-inconsistent, and how it is also inconsistent with not only the Bible, but with other Mormon scripture (e.g., The Pearl of Great Price, and Doctrine and Covenants.)